1) Field of the Invention
This invention relates generally to fabrication of a semiconductor device and more particularly to a carrier and assembly method for ball grid array packages that replace manual flipping of ball grid array substrates during assembly with flipping the carrier.
2) Description of the Prior Art
Conventionally, Auer boats by Auer Precision Co., Inc. of Mesa, Ariz., are used to hold substrates during processing of ball grid array packages, such as FEBGA and EBGA. Substrates for the ball grid array packages are placed in an Auer boat prior to die attach. The substrates are manually flipped prior to marking. They are manually flipped again prior to ball attach. The manual flipping steps are time consuming, typically requiring 30 to 35 minutes per 200 unit lot. Also, the manual handling operations are a significant cause of quality problems, such as handling damage, electrostatic discharge, and misalignment.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following patents.
U.S. Pat. No. 5,695,331 (Nutter) shows a multiple width boat carrier. The carrier is adjustable to accommodate various size IC boats.
U.S. Pat. No. 5,843,808 (Kamezos) shows a method for handling TAB grid arrays using a part of the package known as a stiffener as a carrier during assembly.
It is an object of the present invention to provide a boat and method for holding substrates during ball grid array package fabrication wherein the boat can be flipped rather than manually flipping each substrate.
It is another object of the present invention to provide a boat and method for assembling ball grid array packages wherein the substrates are biases by spring force to reduce dimensional variation during assembly.
To accomplish the above objectives, the present invention provides a boat and method for holding substrates during ball grid array package assembly. The boat comprises a base and one or more spring locks. The base has one or more openings which provide access to both faces of said substrates. The base has bottom supports protruding into the openings to retain the substrates from below and top supports protruding into the openings to retain the substrates from above. The spring locks apply lateral pressure to the substrates forcing the substrates over the bottom supports and under the top supports, whereby the boat can be flipped with the substrates retained between the top supports and the bottom supports. In one embodiment, substrates are installed in the boat, and the entire boat is flipped when the opposite face needs to be accessed, rather than manually flipping each substrate.
The present invention provides considerable improvement over the prior art. By providing access to the opposite face of a substrate by flipping the entire boat rather than manually flipping each substrate, the present invention reduces process time, and reduces quality defects caused by manually handling the substrates. Also, because the substrate is biased against one corner of the opening, alignment tolerance stack-up is reduced.
The present invention achieves these benefits in the context of known process technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.